Method and unit for simultaneously forming multiple tobacco mats

ABSTRACT

A method and unit for simultaneously forming multiple tobacco mats on a multiple-rod cigarette manufacturing machine, whereby an input stream of shredded tobacco is fed to a switch conduit selectively alignable with the inputs of at least two downflow conduits, each of which communicates via a respective carding assembly with a respective upflow conduit closed by a respective conveyor belt for a respective tobacco mat; the switch conduit being switched between positions selectively aligned with the downflow conduits in response to a command signal generated in function of the tobacco level in the downflow conduits.

[0001] The present invention relates to a method and unit for simultaneously forming multiple tobacco mats on a multiple-rod cigarette manufacturing machine.

BACKGROUND OF THE INVENTION

[0002] As is known, for example, from U.S. Pat. No. 4,336,812 and U.S. Pat. No. 4,418,705, on multiple-rod machines in general, and dual-rod machines in particular, an input stream of shredded tobacco is fed to a downflow conduit, the bottom end of which has a wedge-shaped partition member defining the inputs of two conduits, each of which communicates, via a respective carding assembly, with a respective upflow conduit closed by a respective conveyor belt for a respective mat of tobacco.

[0003] In known multiple-rod machines of the type described above, the partition member normally divides the input stream of shredded tobacco into substreams equal in number to the upflow conduits to form an equal number of tobacco mats, which should theoretically be identical. In actual fact, however, identical mats, which presuppose a homogenous input stream of shredded tobacco across its whole section, are difficult to achieve, and cigarettes formed by cutting rods produced from different tobacco mats invariably differ slightly.

[0004] EP-1364588-A1 was filed before, but published after the date of filing of the present application and discloses an arrangement for the formation of at least two tobacco rods in a cigarette rod making machine. In particular, according to EP-1364588-A1 an input stream of shredded tobacco is fed to a switch conduit selectively alignable with the inputs of two downflow conduits, each of which communicates via a respective carding assembly with a respective upflow conduit closed by a respective conveyor belt for a respective tobacco mat; the switch conduit being switched between positions selectively aligned with the downflow conduits in response to a clock signal of predetermined frequency.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide a method of forming mats of shredded tobacco on a multiple-rod cigarette manufacturing machine, in particular a dual-rod machine, designed to minimize the aforementioned drawback, and which provides for forming substantially identical mats of shredded tobacco.

[0006] According to the present invention, there is provided a method of forming mats of shredded tobacco on a multiple-rod cigarette manufacturing machine, as claimed in claim 1 and, preferably, in any one of the following Claims depending directly or indirectly on claim 1.

[0007] According to the present invention, there is also provided a unit for forming mats of shredded tobacco on a multiple-rod cigarette manufacturing machine, as claimed in claim 4 and, preferably, in any one of the following Claims depending directly or indirectly on claim 4.

BRIEF DESCRIPTION OF THE DRAWING

[0008] The present invention will be described by way of example with reference to the accompanying drawing, which shows a schematic cross section of a preferred, non-limiting embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0009] Number 1 in the accompanying drawing indicates as a whole a dual-rod cigarette manufacturing machine, which comprises an input portion defined by a unit 2 for forming two mats 3 of shredded tobacco on the underside surface of respective parallel conveyor belts 4 made of material permeable to air, and which run directly beneath respective suction boxes 5 for retaining mats 3 on respective conveyor belts 4 by suction.

[0010] Unit 2 comprises a loading hopper 6 for an input stream 7 of shredded tobacco fed to the top of hopper 6 by a known tank conveyor 8. Beneath hopper 6, unit 2 comprises two side by side, substantially parallel downflow conduits 9 in a plane parallel to the drawing plane. Each downflow conduit 9 is closed at the bottom by a respective carding assembly 10 comprising a carding roller 11 rotating about an axis 12 in a direction 13, and a known thrower roller 14 substantially tangent to respective carding roller 11 and rotating about an axis 15 parallel to axis 12 in an opposite direction 16 to direction 13. When the relative carding assembly 10 is running, each downflow conduit 9 communicates, via relative carding assembly 10, with the bottom end of a relative upflow conduit 17 closed at the top output end by relative conveyor belt 4.

[0011] Along a curved input portion of each upflow conduit 17, a respective intermediate partition 18 defines, to the side of the input end of relative upflow conduit 17, a respective conduit 19, which flows at the top into relative upflow conduit 17 at a given distance from relative conveyor belt 4, and communicates at the bottom with a respective outlet of a compressed air supply circuit 20.

[0012] Flow of the shredded tobacco from hopper 6 to downflow conduits 9 is controlled by an oscillating switch device 21 comprising a switch conduit 22 alignable selectively with the inputs of the two downflow conduits 9. For which purpose, switch conduit 22 extends between two fixed walls 23 (only one shown) parallel to the plane of the accompanying drawing; and switch device 21 comprises two valve members 24 laterally defining switch conduit 22 and forming the cranks of an articulated parallelogram 25, which also comprises a connecting rod 26 connecting the two valve members 24. Each valve member 24, in section, is substantially in the form of an isosceles triangle, and is hinged at a top vertex to fixed walls 23, which define the frame of articulated parallelogram 25, to oscillate about a respective axis 27 parallel to axes 12 and 15. Valve members 24 are defined laterally by respective flat facing surfaces 28, which are maintained parallel by connecting rod 26 and define, between them and together with fixed walls 23, switch conduit 22. At the bottom end opposite respective axis 27, each valve member 24 is defined by a cylindrical surface portion 29, which, as switch device 21 oscillates, closes a respective downflow conduit 9 when switch conduit 22 is aligned with the other downflow conduit 9.

[0013] Switch device 21 is powered by a motor 30, which is connected to one of the two axes 27 to oscillate articulated parallelogram 25 between two positions aligning switch conduit 22 with one or the other of the two downflow conduits 9, and is controlled by a logic unit 31, which activates motor 30 to switch conduit 22 between said two positions following the emission of a “minimum level” signal and “maximum level” signal emitted by a level detecting device 32 comprising a number of sensors 33 along each downflow conduit 9.

[0014] In actual use, the switch is made when the level of shredded tobacco in the downflow conduit 9 not being supplied at the time reaches the “minimum level”; or after a given supply time of one of downflow conduits 9, providing the other downflow conduit 9 in the meantime does not reach the “minimum level”; or when the downflow conduit 9 being supplied reaches the “maximum level”.

[0015] In connection with the above, it should be pointed out that the whole of input stream 7 is supplied by switch device 21 to either one of downflow conduits 9 at all times, and at no time undergoes any longitudinal division which might result in differences in the streams fed by upflow conduits 17 to respective conveyor belts 4. 

1) A method of simultaneously forming multiple mats (3) of tobacco on a multiple-rod cigarette manufacturing machine (1); the method comprising the step of: feeding an input stream (7) of shredded tobacco to a switch conduit (22) selectively alignable with the inputs of at least two downflow conduits (9), each of which communicates via a respective carding assembly (10) with a respective upflow conduit (17) closed by a respective conveyor belt (4) for a respective mat (3) of tobacco; determining the tobacco level, at least one said downflow conduit (9); generating a command signal in function of the tobacco level; and switching the switch conduit (22) between positions selectively aligned with the downflow conduits (9) in response to said command signal. 2) A method as claimed in claim 1, wherein said command signal comprises a “minimum level” signal emitted upon a given minimum level being reached in one of said downflow conduits (9). 3) A method as claimed in claim 1, wherein said command signal comprises a “maximum level” signal emitted upon a given maximum level being reached in one of said downflow conduits (9). 4) A unit for simultaneously forming multiple mats (3) of tobacco on a multiple-rod cigarette manufacturing machine (1); the unit (2) comprising an input hopper (6) for shredded tobacco, at least two downflow conduits (9), two upflow conduits (17), each connected to a respective said downflow conduit (9), a carding assembly (10) interposed between each downflow conduit (9) and the relative upflow conduit (17), and a conveyor belt (4) for a respective mat (3) of tobacco, located at an output end of each upflow conduit (17); the unit (2) being characterized by comprising a switch device (21) interposed between said input hopper (6) and the downflow conduits (9), and in turn comprising a switch conduit (22) selectively alignable with respective inputs of the downflow conduits (9); control means (31) being provided to switch the switch conduit (22) between positions selectively aligned with said downflow conduits (9) in response to a command signal; and detecting device (32) being provided for determining the tobacco level at least one said downflow conduit (9) and for generating the command signal in function of the tobacco level. 5) A unit as claimed in claim 4, wherein said switch device (21) comprises two side by side valve members (24), which together define said switch conduit (22) and are mounted to oscillate about respective parallel axes (27) to switch said switch conduit (22) between said positions selectively aligned with said downflow conduits (9), and at the same time to close whichever one of said downflow conduits (9) is not aligned with the switch conduit (22). 6) A unit as claimed in claim 4, wherein said switch device (21) comprises two side by side valve members (24), which together define said switch conduit (22) and constitute the cranks of an articulated parallelogram (25) also comprising a connecting rod (26) connecting said two valve members (24); said two valve members (24) being mounted to oscillate, under the control of drive means (30), about respective parallel axes (27). 7) A unit as claimed in claim 5, wherein each said valve member (24), in section, is substantially in the form of an isosceles triangle mounted with one vertex facing upwards and to oscillate about the respective said axis (27) located at said vertex; each valve member (24) being bounded, on the opposite side to said vertex, by a cylindrical surface portion (29) which, as said switch device (21) oscillates, closes a respective downflow conduit (9) when said switch conduit (22) is aligned with the other said downflow conduit (9). 8) A unit as claimed in claim 4, wherein for each said downflow conduit (9) the detecting device (32) is able to emit a “minimum level” signal of the tobacco level. 9) A unit as claimed in claim 4, wherein for each said downflow conduit (9) the detecting device (32) is able to emit “maximum level” signal of the tobacco level. 